A Tool for Integer Homology Computation: Lambda-At Model

In this paper, we formalize the notion of lambda-AT-model (where $\lambda$ is a non-null integer) for a given chain complex, which allows the computation of homological information in the integer domain avoiding using the Smith Normal Form of the boundary matrices. We present an algorithm for computing such a model, obtaining Betti numbers, the prime numbers p involved in the invariant factors of the torsion subgroup of homology, the amount of invariant factors that are a power of p and a set of representative cycles of generators of homology mod p, for each p. Moreover, we establish the minimum valid lambda for such a construction, what cuts down the computational costs related to the torsion subgroup. The tools described here are useful to determine topological information of nD structured objects such as simplicial, cubical or simploidal complexes and are applicable to extract such an information from digital pictures.Comment: Journal Image and Vision Computing, Volume 27 Issue 7, June, 200

Are silica defences in grasses driving vole population cycles?

Understanding the factors that drive species population dynamics is fundamental to biology. Cyclic populations of microtine rodents have been the most intensively studied to date, yet there remains great uncertainty over the mechanisms determining the dynamics of most of these populations. For one such population, we present preliminary evidence for a novel mechanism by which herbivore-induced reductions in plant quality alter herbivore life-history parameters and subsequent population growth. We tested the effect of high silica levels on the population growth and individual performance of voles (Microtus agrestis) reared on their winter food plant (Deschampsia caespitosa). In sites where the vole population density was high, silica levels in D. caespitosa leaves collected several months later were also high and vole populations subsequently declined; in sites where the vole densities were low, levels of silica were low and population density increased. High silica levels in their food reduced vole body mass by 0.5% a day. We argue that silica-based defences in grasses may play a key role in driving vole population cycles

The effect of medium-term heat acclimation on endurance performance in a temperate environment

We investigated whether an 11-day heat acclimation programme (HA) enhanced endurance performance in a temperate environment, and the mechanisms underpinning any ergogenic effect. Twenty-four males (V̇O2max: 56.7±7.5 mL∙kg-1∙min-1) completed either: i) HA consisting of 11 consecutive daily exercise sessions (60-90 minutes·day-1; n=16) in a hot environment (40°C, 50% RH) or; ii) duration and exertion matched exercise in cool conditions (CON; n=8 [11°C, 60% RH]). Before and after each programme power at lactate threshold, mechanical efficiency, VO2max, peak power output (PPO) and work done during a 30-minute cycle trial (T30) were determined under temperate conditions (22°C, 50% RH). HA reduced resting (-0.34±0.30°C) and exercising (-0.43±0.30°C) rectal temperature, and increased whole-body sweating (+0.37±0.31 L·hr-1) (all P≤0.001), with no change in CON. Plasma volume increased in HA (10.1±7.2%, P<0.001) and CON (7.2±6.3%, P=0.015) with no between-groups difference, whereas exercise heart rate reduced in both groups, but to a greater extent in HA (-20±11 b·min-1) than CON (-6±4 b·min-1). VO2max, lactate threshold and mechanical efficiency were unaffected by HA. PPO increased in both groups (+14±18W), but this was not related to alterations in any of the performance or thermal variables, and T30 performance was unchanged in either group (HA: Pre=417±90 vs. Post=427±83 kJ; CON: Pre=418±63 vs. Post=423±56 kJ). In conclusion, 11-days HA induces thermophysiological adaptations, but does not alter the key determinants of endurance performance. In trained males, the effect of HA on endurance performance in temperate conditions is no greater than that elicited by exertion and duration matched exercise training in cool conditions

Inter-individual variation in the adaptive response to heat acclimation

Aim: To investigate inter-individual variance in adaptive responses to heat acclimation (HA).Methods: 17 males (VO2max=58.8(8.4) ml·kg-1·min-1) undertook 10-days (exercise + heat stress [40°C, 50%RH]) HA. Adaptation was assessed by heat stress tests (HST; 60–minutes cycling, 35% peak power output) pre- and post-HA. Results: Inter-individual variability was evident in adaptive responses e.g. mean(range) reduction in end-exercise Tre=-0.70(-0.20 to - 1.32)°C, but, in the main, the variance in adaptation was unrelated across indices (thermal sudomotor, cardiovascular, haematological), indicating independence between adaptation indices. Variance in adaptive responses was not correlated with aerobic capacity, history of previous HA, or the accrued thermal-dose. Some responses to the initial HST were related to the subsequent adaptations e.g. ∆T̅sk during the initial HST and the reduction in the within HST ΔTre after HA (r=-0.676), but responses to the initial HST may also have been influenced by HST design e.g. ΔTre correlated with metabolic heat production (r=0.609). Metabolic heat production also correlated with the reduction in the within HST ΔTre after HA (r=-0.514). Summary: HA indices are mainly independent; ‘low’, or ‘high’, responders on one index do not necessarily demonstrate similar response across other indices. Variance in HA responses was not related to aerobic capacity, previous HA, or thermal-dose. Thermo-physiological responses to a HST might identify individuals who will benefit from HA. However, some initial responses are influenced by HST design, which may also affect the scope for demonstrating adaption. Conclusion: Variance in the HA response remains largely unaccounted for and future studies should identify factors contributing to this variance

Inter-individual variation in the adaptive response to heat acclimation; impact on temperate performance

Introduction: Typical heat acclimation (HA) responses are well characterised at the cohort level, however, individual data demonstrate considerable heterogeneity. Recent research suggests that HA indicies are independent and not influenced by aerobic capacity, previous HA or thermal dose. However, some baseline responses may be useful in estimating the potential benefits that an individual may obtain from HA. It remains to be establised whether the extent of individual HA will translate to aspects of individual endurance performance and thermophysiological indicies in temperate conditions, and if these can be related to any prior variables

Coexistence of double alternating antiferromagnetic chains in (VO)_2P_2O_7 : NMR study

Nuclear magnetic resonance (NMR) of 31P and 51V nuclei has been measured in a spin-1/2 alternating-chain compound (VO)_2P_2O_7. By analyzing the temperature variation of the 31P NMR spectra, we have found that (VO)_2P_2O_7 has two independent spin components with different spin-gap energies. The spin gaps are determined from the temperature dependence of the shifts at 31P and 51V sites to be 35 K and 68 K, which are in excellent agreement with those observed in the recent inelastic neutron scattering experiments [A.W. Garrett et al., Phys. Rev. Lett. 79, 745 (1997)]. This suggests that (VO)_2P_2O_7 is composed of two magnetic subsystems showing distinct magnetic excitations, which are associated with the two crystallographically-inequivalent V chains running along the b axis. The difference of the spin-gap energies between the chains is attributed to the small differences in the V-V distances, which may result in the different exchange alternation in each magnetic chain. The exchange interactions in each alternating chain are estimated and are discussed based on the empirical relation between the exchange interaction and the interatomic distance.Comment: 10 pages, 11 embedded eps figures, REVTeX, Submitted to Phys. Rev.

Effects of acute or chronic heat exposure, exercise and dehydration on plasma cortisol, IL-6 and CRP levels in trained males

This study examined the acute and chronic effects of euhydrated and hypohydrated heat exposure, on biomarkers of stress and inflammation. Eight trained males [mean (SD) age: 21 (3) y; mass: 77.30 (4.88) kg; V̇O2max: 56.9 (7.2) mL·kg−1·min−1] undertook two heat acclimation programmes (balanced cross-over design), once drinking to maintain euhydration and once with restricted fluid-intake (permissive dehydration). Days 1, 6, and 11 were 60 min euhydrated exercise-heat stress tests (40 °C; 50 % RH, 35% peak power output), days 2–5 and 7–10 were 90 min, isothermal-strain (target rectal temperature: 38.5 °C) exercise-heat sessions. Plasma was obtained pre- and post- exercise on day 1, 2, and 11 and analysed for cortisol, interleukin-6 (IL-6), and C-reactive protein (CRP). Cortisol and CRP were also assessed on day 6. IL-6 was elevated following the initial (acute) 90 minute isothermal heat strain exercise-heat exposure (day 2) with permissive dehydration ( (pre exercise: 1.0 pg.mL-1 [0.9], post-exercise: 1.8 pg.mL-1 [1.0], P = 0.032) and when euhydrated (pre-exercise: 1.0 pg.mL-1 [1.4], post-exercise: 1.6 pg.mL-1 [2.1], P = 0.048). Plasma cortisol levels were also elevated but only during permissive dehydration (P = 0.032). Body mass loss was strongly correlated with Δcortisol (r = -0.688, P = 0.003). Although there was a trend for post-exercise cortisol to be decreased following both heat acclimation programmes (chronic effects), there were no within or between intervention differences in IL-6 or CRP. In conclusion, acute exercise in the heat increased IL-6 and cortisol only when fluid-intake is restricted. There were no chronic effects of either intervention on biomarkers of inflammation as evidenced by IL-6 and CRP returning to basal level at the end of heat acclimation

The self-regulation skills instrument in transplantation (SSIt):Development and measurement properties of a self-report self-management instrument

Objective: To develop a self-management instrument for organ transplant recipients that incorporates self-regulations skills and to determine its measurement properties. Methods: The instrument includes concepts from social cognitive models: problem awareness, attitude, self-efficacy, motivation, social support, goal setting, goal pursuit, skills and goal affect. The measurement properties were evaluated based on the COSMIN guidelines. Face and content validity were determined through patient assessment, Three-Step Test-Interview and expert assessment using the Content Validity Index. Structural validity and reliability were tested using exploratory factor analysis and Cronbach's alpha. Construct validity was tested by comparing subscales with the Health Education Impact Questionnaire (heiQ). Results: After face and content validity assessment 47 items were entered into the exploratory factor analysis. The analysis showed two meaningful factors, with internal consistency of 0.90 and 0.89. Spearman correlations between the subscales and heiQ were moderate (0.55; 0.46). The final version consists of 21 items, divided into two scales: ‘Setbacks’ and ‘Successes’. Conclusions: The Self-regulation skills instrument in transplantation (SSIt) is a valid and reliable instrument to asses necessary skills for self-management after transplantation and may be useful for other patients as well. Practice implications: Insight into self-regulation competencies can help healthcare professionals to tailor self-management support.</p

The self-regulation skills instrument in transplantation (SSIt):Development and measurement properties of a self-report self-management instrument

Objective: To develop a self-management instrument for organ transplant recipients that incorporates self-regulations skills and to determine its measurement properties. Methods: The instrument includes concepts from social cognitive models: problem awareness, attitude, self-efficacy, motivation, social support, goal setting, goal pursuit, skills and goal affect. The measurement properties were evaluated based on the COSMIN guidelines. Face and content validity were determined through patient assessment, Three-Step Test-Interview and expert assessment using the Content Validity Index. Structural validity and reliability were tested using exploratory factor analysis and Cronbach's alpha. Construct validity was tested by comparing subscales with the Health Education Impact Questionnaire (heiQ). Results: After face and content validity assessment 47 items were entered into the exploratory factor analysis. The analysis showed two meaningful factors, with internal consistency of 0.90 and 0.89. Spearman correlations between the subscales and heiQ were moderate (0.55; 0.46). The final version consists of 21 items, divided into two scales: ‘Setbacks’ and ‘Successes’. Conclusions: The Self-regulation skills instrument in transplantation (SSIt) is a valid and reliable instrument to asses necessary skills for self-management after transplantation and may be useful for other patients as well. Practice implications: Insight into self-regulation competencies can help healthcare professionals to tailor self-management support.</p